The paraoxonase family of genes (PON1, PON2 and PONS) is located on human chromosome 7. HDLassociated PON1 metabolizes organophosphorus (OP) compounds, oxidized lipids, drugs and quorumsensing factors. PON1 polymorphisms affect catalytic efficiency and plasma levels. The consequences of the two PON2 coding region polymorphisms are unknown. PON1 is synthesized in liver and secreted into plasma, whereas PON2 is ubiquitously expressed in tissues, including brain. PON2 does not hydrolyze OPs but has strong antioxidant properties. PON1 status was found to be altered in male Parkinson's patients compared with male control subjects. The proposed studies aim to increase our knowledge of PON1, PON2 and PONS functions in determining susceptibility to environmentally-induced neurotoxicity and neurodegenerative diseases. Specific Aim 1 follows up on our studies on the relationship of PON1 status and susceptibility to OP toxicity in a cohort of Washington State pesticide handlers. In addition to monitoring plasma cholinesterase levels, we will include a novel quantitative mass spectrometric (MS) analysis of protein biomarkers modified by exposures in OP handlers and airline incidents. Specific Aim 2 investigates the interplay of PON1 and carboxylesterase in modulating the toxicity of insecticide mixtures. Specific Aim 3 examines the role of PON1 in modulating prenatal developmental neurotoxicity of chlorpyrifos oxon, where PON1 status of dams is hypothesized to be important for fetal protection. These studies with PON1 null mice and humanized PON1 transgenic mice (tgHuPON1-Q192 &tgHuPON1-R192) include biochemical, behavioral, histopathological and molecular end-points. Specific Aim 4 investigates the role of PONs 1, 2 and 3 and HDL composition in Parkinson's disease (PD). As a follow-up on our previous studies that showed differences in PON1 status in male PD patients compared with controls, we will use an MS-based proteomic approach to examine HDL composition in PD subjects vs. matched controls. Mice lacking PON proteins will also be tested for sensitivity to the dopaminergic neurotoxin MPTP. Specific Aim 5 involves a collaboration with Project 5 to express stable rabbit PON1 in plant systems for remediating OP spills.